1. Field of the Invention
The present invention relates to an X-ray mask which is used in the manufacture of microdevices such as semiconductor integrated circuits to transfer a micropattern onto a wafer, and an X-ray exposure method and apparatus using the same.
2. Related Background Art
Semiconductor integrated circuits continue to be minutely downsized in their feature size year by year. Along with this trend, an exposure apparatus for transferring a circuit pattern onto a wafer is required to transfer increasingly minute circuit patterns. For this reason, the wavelength of exposure light used in exposure apparatuses is gradually becoming shorter, and recently, an exposure apparatus using soft X-rays as a transfer means for the most elaborate circuit patterns has been examined.
Upon transferring the circuit pattern of a semiconductor integrated circuit by exposure, contamination due to foreign matter attached to the exposure mask is a very serious problem. If foreign matter becomes attached to a mask, it is transferred onto the wafer and becomes a defect in the circuit pattern. For this reason, attachment of foreign matter must be prevented as much as possible. In particular, in exposure using soft X-rays, since the transmittance of X-rays through various substances is very low, X-rays cannot be transmitted through even very small foreign matter, thus causing defects.
As the circuit pattern is more downsized, it becomes more difficult to remove foreign matter on the mask or to repair the mask. In X-ray masks, such difficulties are pronounced due to their structures.
The X-ray masks are roughly classified into a transmission type mask and a reflection type mask. In a transmission type mask, since a mask pattern (circuit pattern) is formed on a self-supported film, the mask must be repaired to prevent changes in stress of the self-supported film. On the other hand, in a reflection type mask using a multi-layered film reflection mirror, since the reflection layer has a multilayered structure, the mask must be repaired to preclude any influence on the multilayered structure. These techniques, however, are very difficult to achieve. Hence, attachment of foreign matter must be avoided more carefully in the X-ray masks than the masks used in exposure apparatuses using visible light and ultraviolet rays.
In exposure apparatuses using visible light and ultraviolet rays, a pellicle consisting of an organic thin film such as nitrocellulose, parylene, or the like is often set on the mask so as to prevent attachment of foreign matter. Since the pellicle is set therein, foreign matter can be prevented from becoming attached to the mask and, hence, contamination can be avoided.
In particular, in a projection exposure type exposure apparatus, when the pellicle is set to fall outside the field depth of an imaging optical system, even when foreign matter becomes attached onto the pellicle, it is never transferred onto the wafer, and any foreign matter attached onto the pellicle can be easily removed. For this reason, the yield of transferred patterns can be improved greatly. Also, once mask inspection is done upon setting the pellicle, foreign matter inspection on the pellicle need only be performed from then on.
Therefore, in some examples (Japanese Patent Publication No. 5-88534, Japanese Laid-Open Patent Application No. 5-150445), an X-ray transmission thin film such as a diamond film, an organic thin film, or the like, a so-called pellicle, is set on an X-ray mask as well.
However, since X-ray exposure is normally done in a high vacuum, a reduced pressure atmosphere, or an atmosphere substituted by a gas such as helium with high purity, when a pellicle is set on an X-ray mask, a pressure difference is produced between the dust-proof space inside the pellicle and the surrounding atmosphere, and the pellicle or the mask itself may be destroyed or deformed by the pressure difference.
When the pellicle is set therein, it poses another problem unique to X-rays. That is, the pellicle absorbs X-rays considerably, and the X-ray exposure intensity attenuates.
The present invention has been made to solve the problems of the above-mentioned conventional art, and has as its object to provide an X-ray mask which can attain high-precision exposure while reducing the possibility of mask damage, an exposure method and apparatus using the mask, a device manufacturing method, and the like.
In order to achieve the above object, according to one preferred aspect of the present invention, an X-ray mask is characterized by comprising: a mask pattern; protection means for forming a dust-proof space for protecting the mask pattern; and a hole for ventilating between the dust-proof space and an outer atmosphere.
For example, the X-ray mask comprises a transmission type mask, which comprises an X-ray transparent membrane, on a surface of which the mask pattern is formed, and the protection means is arranged on at least one of a front surface side and a rear surface side of the membrane.
For example, the X-ray mask comprises a reflection type mask, in which a multilayered film reflection layer and the mask pattern are formed on a substrate, and the protection means is arranged on the mask pattern.
For example, the protection member comprises a detachable protection member, or the protection member comprises an X-ray transparent pellicle film.
It is preferable that the protection member be subjected to an antistatic treatment. Also, preferably, the hole has a lid which is free to open/close, or the hole has a filter.
According to another preferred aspect of the present invention, an X-ray mask is characterized by comprising: an X-ray transparent membrane; a mask pattern formed on a surface of the membrane; and protection members formed on both a front surface side and a rear surface side of the membrane and forming a dust-proof space.
According to a preferred aspect of the present invention, an exposure method is characterized by comprising the steps of: preparing an X-ray mask comprising a mask pattern and detachable protection means for forming a dust-proof space for protecting the mask pattern; carrying the X-ray mask with the protection means attached; and exposing the mask pattern to X-rays while the protection means is detached.
The scope of the present invention includes a device manufacturing method for manufacturing a microdevice in processes including the above-mentioned exposure method.
Other objects and aspects of the present invention will become apparent from the following description of the embodiments.